Intrinsic quasar variability and time delay determination in the lensed quasar UM673

Abstract

We present the results of time delay measurements between the A and B components of the gravitationally lensed quasar UM673. The measurements are based on the brightness variations of the quasar components observed with the 1.5‐m telescope of the Maidanak Observatory in the V, R and I bands during the 2003–2005 observational period. The amplitudes of variations in the R band are 0.046 and 0.122 mag for Component A and B, respectively. Due to the short visibility period of UM673, about 3 months in a year, the light curves of the quasar components have large annual gaps. It complicates the time delay estimation. From the cross‐correlation analysis, we find that the brightness variations in component B follow the brightness variations in Component A by about 150 days. We also explore the possibility of measuring the wavelength‐dependent time delay between the brightness variations in the V, R and I bands. We find that in agreement with reprocessing model of quasar variability, the brightness variation at longer wavelengths follows the brightness variations at shorter wavelengths. Finally, we show that the combination of the multiband data corrected for the wavelength‐dependent time delay can help to improve the cross‐correlation analysis of the light curves with large annual gaps.

Flux and color variations of the doubly imaged quasar UM673

“…Moreover, our observations are in good agreement with the previous works carried out by Muñoz et al (1998), Koptelova et al (2010b), and Koptelova et al (2012) in terms of flux variations and color index. We also separated the contribution of the and "B+G" (rhombi) with time, including the data from HST (Muñoz et al 1998), from Nakos et al (2005), from Koptelova et al (2010b) and from the present work.…”

“…7 we compare the evolution of the V − i color index with time, by using the data collected from HST (Muñoz et al 1998), Nakos et al (2005), and Koptelova et al (2010b). An adaptation of recently published data by Koptelova et al (2012) is also shown.…”

“…A "global i" light curve which also includes the results of Muñoz et al (1998), Nakos et al (2005) and Koptelova et al (2010bKoptelova et al ( , 2012) is shown in Fig. 8.…”

“…For a more accurate fitting, we used a bicubic interpolation of the images. Koptelova et al (2010bKoptelova et al ( , 2012 observed UM673 with the VRI filters, and derived the photometry without separately taking into account the magnitude of "B" and that of the lens galaxy "G". As the lens galaxy is located very close to the "B" component, and for comparison with other works, we also calculated the magnitudes of the "B"+"G" components as a simple superposition of their fluxes.…”

Flux and color variations of the quadruply imaged quasar HE 0435-1223

“…Furthermore, Q2237+0305 was the object of deep studies focused on the lens galaxy (Poindexter & Kochanek 2010b), and on the inclination of the accretion disk (Poindexter & Kochanek 2010a). Another example of multi-epoch multi-band observations is given by UM673/Q0142-100, observed in the Gunn i and Cousins V filters between 1998 and 1999 (Nakos et al 2005) (Koptelova et al 2010). Unlike for these objects, no systematic multi-band photometry has ever been carried out for HE0435-1223.…”